Interpretive Summary: Soil erosion by water is a continuing threat to our natural resources and to agricultural crop production. In order to estimate the amount of soil being lost from fields during rain storms, and the amount of eroded sediment that leaves these fields and ends up in off-site streams and other water bodies, some type of computer simulation model is usually applied. Models are used because they can rapidly evaluate current and alternative land management practices for a specific location, slope shape, and soil type, and are much less expensive and time-consuming compared to impractical long-term field monitoring. However, for typical users to successfully apply a soil erosion model, they need guidance on how to set up a simulation, and how to calibrate and validate the model to be confident that it is giving good predictions. This paper provides information on the Water Erosion Prediction Project (WEPP) model, with detailed information on how to set up simulations for small field areas as well as for larger farm watersheds. In addition to identifying input parameters to use during model calibration and validation, it also provides two case studies of WEPP applications by other researchers. This work impacts other scientists, university faculty, students, action agency personnel and any user involved in applying the WEPP model. Understanding and following correct model application guidelines are essential for successful and accurate WEPP model use.

Technical Abstract:
The Water Erosion Prediction Project (WEPP) model is a process-based, continuous simulation, distributed parameter, hydrologic and soil erosion prediction system. It has been developed over the past 25 years to allow for easy application to a large number of land management scenarios. Most general or field agency users of WEPP rely upon existing or special databases and/or interfaces that have been developed, tested, and verified by others. This paper describes WEPP model calibration and validation procedures, under ideal situations (where all necessary input data and runoff/sediment observations are available), as well as under more typical and less ideal conditions. Two case study applications of the model from the literature are highlighted and discussed in detail as examples of single storm hillslope profile and continuous simulation watershed applications. Current and future development efforts on WEPP are also described.